Messages in this thread Patch in this message | | | From | Jeff Moyer <> | Date | Mon, 23 Jan 2006 14:16:07 -0500 | Subject | [patch] fix O_DIRECT read of last block in a sparse file |
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Hi,
Currently, if you open a file O_DIRECT, truncate it to a size that is not a multiple of the disk block size, and then try to read the last block in the file, the read will return 0. The problem is in do_direct_IO, here:
/* Handle holes */ if (!buffer_mapped(map_bh)) { char *kaddr;
...
if (dio->block_in_file >= i_size_read(dio->inode)>>blkbits) { /* We hit eof */ page_cache_release(page); goto out; }
We shift off any remaining bytes in the final block of the I/O, resulting in a 0-sized read. I've attached a patch that fixes this. I'm not happy about how ugly the math is getting, so suggestions are more than welcome.
I've tested this with a simple program that performs the steps outlined for reproducing the problem above. Without the patch, we get a 0-sized result from read. With the patch, we get the correct return value from the short read.
Thanks,
Jeff
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
--- linux-2.6.16-rc1-mm1/fs/direct-io.c.orig 2006-01-19 15:45:50.000000000 -0500 +++ linux-2.6.16-rc1-mm1/fs/direct-io.c 2006-01-19 16:09:33.000000000 -0500 @@ -857,6 +857,7 @@ do_holes: /* Handle holes */ if (!buffer_mapped(map_bh)) { char *kaddr; + loff_t i_size = i_size_read(dio->inode); /* AKPM: eargh, -ENOTBLK is a hack */ if (dio->rw == WRITE) { @@ -864,8 +865,10 @@ do_holes: return -ENOTBLK; } - if (dio->block_in_file >= - i_size_read(dio->inode)>>blkbits) { + /* Be sure to account for a partial block as + * the last block in the file */ + if (dio->block_in_file >= i_size >> blkbits && + !(i_size & ~((1<<blkbits)-1))) { /* We hit eof */ page_cache_release(page); goto out; - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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